Oxygen radicals are known to cause a number of disruptive processes at the cellular level. These include lipid peroxidation, alterations of enzyme activity, cleavage of DNA, cell mortality, and polymerization of polysaccharides. Furthermore, oxygen radicals can be generated by a number of physical or biological processes (e.g., enzymatically, photochemically, radiochemically, etc.). It is now well recognized that oxygen radicals are important mediators in the toxicity of chemical substances. For example, compounds which produce oxygen radicals have been shown to act as tumor promoters. Multiple defense mechanisms have evolved for coping with oxidant toxicity at the cellular level. Enzymes such as superoxide dismutase, catalase and other peroxidase (e.g., glutathione peroxidase) remove oxygen radicals and anions. Also reactive radicals such as OH.sup.. and O.sub.2.- can be removed by small radical-trapping molecules such as Vitamin A, C and E and by thiols such as reduced glutathione.
Therefore, a need exists for methods to determine the ability of mammalian cells to resist the internalization of free radicals, such as the oxygenderived free radicals generated by the action of ultraviolet (UV) light on the skin. Such methods can be used to determine the efficacy of therapeutic antioxidants and to diagnose pathologies which alter oxidant removal pathways in vivo.